DETERMINATION OF WATER CONTENT- DRY DENSITY RELATION (HEAVY COMPACTION)

STANDARD

IS: 2720 (Part 8) 1983.

OBJECTIVE

To determine the required amount of water to be used when compacting the

soil in the field and the resulting degree of denseness, which can be expected

from compaction at optimum moisture content.

APPARATUS

Cylindrical metal mould shall be either of 100mm diameter and 1000cm3 volume

or 150mm diameter and 2250cm3 volume and shall confirm to IS: 10074 – 1982.

Balance of capacity 500grams and sensitivity 0.01gram.

Balance of capacity 15Kg and sensitivity one gram.

Thermostatically controlled oven with capacity up to 250 0C.

Airtight containers.

Steel straight edge about 30cm in length and having one beveled edge.

4.75mm, 19mm and 37.5mm IS sieves confirming to IS 460 (Part 1).

Mixing tools such as tray or pan, spoon, trowel and spatula or suitable mechanical

device for thoroughly mixing the sample of soil with additions of water.

Heavy compaction rammer confirming to IS: 9189 -1979.

PROCEDURE

Take a representative sample of air dried soil of about 5 kg (soil not susceptible to

crushing during compaction) or 3 kg from 15 kg sample (soil susceptible to crushing

during compaction) passing through 19mm IS sieve and mix thoroughly with a

suitable amount of water depending on the type of soil, generally 4 to 6 percent for

sandy and gravelly soils and plastic limit minus 8% to 10% for cohesive soils.

For soils susceptible to crushing during compaction take different samples for every

determination and for soils not susceptible to crushing during compaction use the

same sample for all the determinations.

Weigh the 1000cc capacity mould with base plate attached and with out extension

to the nearest gram (m1).

Place the mould on a solid base such as a concrete floor or plinth and compact the

moist soil into the mould, with the extension attached in 5 layers of approximately

equal mass, each layer being given 25 blows with the 4.90kg hammer dropped

from a height of 450mm above the soil.

Distribute the blows uniformly on each layer.

The amount of soil used shall be sufficient to fill the mould leaving not more than

about 6mm to be struck off when the extension is removed.

Compaction of soil in to mould

Remove the extension and carefully level the compacted soil to the top of mould

by means of straight edge.

Weigh the mould and the soil to the nearest gram (m2). Remove the compacted

soil from the mould and place on the mixing tray.

Collect a representative sample from the soil in the tray and keep in the oven for

24 hours maintained at a temperature of 1050 to 1100 C to determine the moisture

content (W).

Compacting soil containing coarse material up to 37.50 mm size

Take representative sample of material passing through 37.50 mm IS sieve.

Compact the material in 2250 cm3 volume of mould in five layers each layer being

given 55 blows with 4.90 kg rammer dropped from a height of 450mm above the

soil.

The remaining procedure is same as described above for 1000cc mould.

In all the above cases make at least five determinations and the range of moisture

content shall be such that the optimum moisture content at which the maximum

dry density occurs is within that range.

CALCULATIONS

Calculate the bulk density w in g / cm3 of each compacted specimen from the

equation,

w = (m2 – m1) / Vm

m1 = Weight of mould with base plate.

m2 = Weight of mould with compacted soil.

Vm = Volume of mould in cm3.

Calculate the dry density d in g/cm3 from the equation,

d = w / (1+W/100)

w = Bulk density

W = % of moisture content

REPORT

Plot the values obtained for each determination on a graph representing moisture

content on x-axis and dry density on y-axis.

Draw a smooth curve through the resulting points and determine the position of

the maximum in the curve.

Report the dry density corresponding to the maximum point to the nearest 0.01.

Report the percentage corresponding to the maximum dry density i.e. optimum

moisture content to the nearest 0.2 %for values below 5% and to the nearest 0.5%

for values from 5 to 10% and to nearest whole number for values exceeding 10 %.

PRECAUTION

With clays of high plasticity or where hand mixing is employed, it may be difficult

to distribute the moisture uniformly through out the air dried soil by mixing alone,

So it may be necessary to preserve the mixed sample in a sealed container for a

minimum period of about 16 hours before conducting the test.